Firefox 117 for developers

No notable changes.

• The CSS Nesting module is now supported in Firefox, along with the & nesting selector. This allows developers to write nested CSS, which helps with the readability, modularity, and maintainability of CSS stylesheets. It also potentially helps reduce CSS file size, decreasing download sizes. (Firefox bug 1835066, Firefox bug 1840781)
• The math-style and math-depth properties are now supported, as well as the math value for the font-size property (Firefox bug 1845516).
• The contain-intrinsic-size: auto none syntax is now supported, which allows for using the last-remembered size of an element if possible and falls back to contain-intrinsic-size: none otherwise. This is useful for grid and multi-column layouts to allow elements to be laid out as though they have no contents instead of 0px height (Firefox bug 1835813).

No notable changes.

• Inline SVGs now support <script> elements with type="module", defer, and async attributes. This allows SVGs to use modern JavaScript features, including ES modules, and to load scripts asynchronously (Firefox bug 1839954).

• Fixed a bug where the Content-Security-Policy 'strict-dynamic' source expression was not being enforced in default-src directives. The behavior now matches the specification where default-src directive values are used as a fallback when script-src is not provided (Firefox bug 1313937).
• The Range header is now a CORS-safelisted request header when the value is a single byte range (e.g., bytes=100-200). This allows the Range header to be used in cross-origin requests without triggering a preflight request, which is useful for requesting media and resuming downloads (Firefox bug 1733981).

• The CanvasRenderingContext2D.getContextAttributes() method can now be used to get the 2D context attributes being used by the browser (Firefox bug 1517786).
• The ReadableStream.from() static member is now supported, allowing developers to construct a readable stream from any iterable or async iterable object (Firefox bug 1772772).
• WebRTC Encoded Transforms are now supported, allowing web applications to modify incoming and outgoing WebRTC encoded video and audio frames using a TransformStream running in a worker. The supported interfaces include: RTCRtpScriptTransform, RTCRtpScriptTransformer, RTCRtpSender.transform, RTCRtpReceiver.transform, RTCEncodedVideoFrame, and RTCEncodedAudioFrame, and the RTCTransformEvent and worker rtctransform event (Firefox bug 1631263).
• CSSStyleRule now inherits from CSSGroupingRule instead of directly from CSSRule. As a result, it additionally implements the property cssRules and the methods deleteRule() and insertRule() (Firefox bug 1846251).

WebDriver BiDi

• Added the browser.close command that allows users to terminate all WebDriver sessions and close the browser (Firefox bug 1829334).
• Added the browsingContext.setViewport command that allows users to change the dimensions of a top level browsing context (Firefox bug 1838664).
• Added the browsingContext.fragmentNavigated event which is emitted for same-document navigations (Firefox bug 1841039).
• Added support for the background argument of the browsingContext.create command, which will force the new context to be created in the background. This argument is optional and defaults to false, meaning that browsingContext.create now opens new contexts in the foreground by default (Firefox bug 1843507).
• Added support for the clip argument of the browsingContext.captureScreenshot command, which allows to restrict the screenshot either to a specific area or to an element. When clipping to an element, you can optionally scroll the element into view before taking the screenshot (Firefox bug 1840998).
• All commands and events related to a navigation will now provide a navigation id, which is a UUID identifying a specific navigation. This property is available in the browsingContext.navigate response, in the browsingContext.load, browsingContext.domContentLoaded, browsingContext.fragmentNavigated events, as well as in all network events created for a navigation request (Firefox bug 1763122, Firefox bug 1789484, Firefox bug 1805405).
• headers and cookies in network events are now serialized as network.BytesValue, which will provide a better support for non-UTF8 values (Firefox bug 1842619).
• The browsingContext.create command will now wait until the created context has a valid size (Firefox bug 1847044).

• The Network Monitor now shows information about proxied requests, including the proxy address, the proxy status, and the proxy HTTP version in the Headers tab (Firefox bug 1707192).
• The area selected by the Measuring Tool can now be resized and moved using keyboard shortcuts. Pressing the arrow keys moves the selected area, while pressing Ctrl + arrow keys (or Cmd + arrow keys on a Mac) resizes the selected area. Holding down the Shift key accelerates the moving and resizing actions when using these key combinations (Firefox bug 1262782).
• Properties that are not supported in highlight pseudo-elements (::highlight(), ::target-text, ::spelling-error, ::grammar-error, and ::selection) are now reported in the Page Inspector CSS rules panel (Firefox bug 1842157).